content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.flowable.subscribers;
  
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.Subscription;
  
  import hu.akarnokd.reactivestreams.extensions.RelaxedSubscriber;
  import io.reactivex.common.Disposable;
  import io.reactivex.common.internal.disposables.ListCompositeDisposable;
  import io.reactivex.common.internal.functions.ObjectHelper;
  import io.reactivex.flowable.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.flowable.internal.utils.EndSubscriberHelper;
  
  /**
   * An abstract Subscriber that allows asynchronous cancellation of its
   * subscription and associated resources.
   *
   * <p>All pre-implemented final methods are thread-safe.
   *
   * <p>To release the associated resources, one has to call {@link #dispose()}
   * in {@code onError()} and {@code onComplete()} explicitly.
   *
   * <p>Use {@link #add(Disposable)} to associate resources (as {@link io.reactivex.common.Disposable Disposable}s)
   * with this {@code ResourceSubscriber} that will be cleaned up when {@link #dispose()} is called.
   * Removing previously associated resources is not possible but one can create a
   * {@link io.reactivex.common.disposables.CompositeDisposable CompositeDisposable}, associate it with this
   * {@code ResourceSubscriber} and then add/remove resources to/from the {@code CompositeDisposable}
   * freely.
   *
   * <p>The default {@link #onStart()} requests Long.MAX_VALUE by default. Override
   * the method to request a custom <em>positive</em> amount. Use the protected {@link #request(long)}
   * to request more items and {@link #dispose()} to cancel the sequence from within an
   * {@code onNext} implementation.
   *
   * <p>Note that calling {@link #request(long)} from {@link #onStart()} may trigger
   * an immediate, asynchronous emission of data to {@link #onNext(Object)}. Make sure
   * all initialization happens before the call to {@code request()} in {@code onStart()}.
   * Calling {@link #request(long)} inside {@link #onNext(Object)} can happen at any time
   * because by design, {@code onNext} calls from upstream are non-reentrant and non-overlapping.
   *
   * <p>Like all other consumers, {@code ResourceSubscriber} can be subscribed only once.
   * Any subsequent attempt to subscribe it to a new source will yield an
   * {@link IllegalStateException} with message {@code "It is not allowed to subscribe with a(n) <class name> multiple times."}.
   *
   * <p>Implementation of {@link #onStart()}, {@link #onNext(Object)}, {@link #onError(Throwable)}
   * and {@link #onComplete()} are not allowed to throw any unchecked exceptions.
   * If for some reason this can't be avoided, use {@link io.reactivex.flowable.Flowable#safeSubscribe(org.reactivestreams.Subscriber)}
   * instead of the standard {@code subscribe()} method.
   *
   * <p>Example<pre><code>
   * Disposable d =
   *     Flowable.range(1, 5)
   *     .subscribeWith(new ResourceSubscriber&lt;Integer&gt;() {
   *         &#64;Override public void onStart() {
   *             add(Schedulers.single()
   *                 .scheduleDirect(() -&gt; System.out.println("Time!"),
   *                     2, TimeUnit.SECONDS));
   *             request(1);
   *         }
   *         &#64;Override public void onNext(Integer t) {
   *             if (t == 3) {
   *                 dispose();
   *             }
   *             System.out.println(t);
   *             request(1);
   *         }
   *         &#64;Override public void onError(Throwable t) {
   *             t.printStackTrace();
   *             dispose();
   *         }
   *         &#64;Override public void onComplete() {
   *             System.out.println("Done!");
   *             dispose();
   *         }
   *     });
   * // ...
   * d.dispose();
   * </code></pre>
   *
   * @param <T> the value type
   */
  public abstract class ResourceSubscriber<T> implements RelaxedSubscriber<T>, Disposable {
      /** The active subscription. */
      private final AtomicReference<Subscription> s = new AtomicReference<Subscription>();
  
      /** The resource composite, can never be null. */
      private final ListCompositeDisposable resources = new ListCompositeDisposable();
  
      /** Remembers the request(n) counts until a subscription arrives. */
      private final AtomicLong missedRequested = new AtomicLong();
  
      /**
       * Adds a resource to this AsyncObserver.
       *
       * @param resource the resource to add
       *
       * @throws NullPointerException if resource is null
       */
      public final void add(Disposable resource) {
          ObjectHelper.requireNonNull(resource, "resource is null");
          resources.add(resource);
      }
  
      @Override
      public final void onSubscribe(Subscription s) {
          if (EndSubscriberHelper.setOnce(this.s, s, getClass())) {
              long r = missedRequested.getAndSet(0L);
              if (r != 0L) {
                  s.request(r);
              }
              onStart();
          }
      }
  
      /**
       * Called once the upstream sets a Subscription on this AsyncObserver.
       *
       * <p>You can perform initialization at this moment. The default
       * implementation requests Long.MAX_VALUE from upstream.
       */
      protected void onStart() {
          request(Long.MAX_VALUE);
      }
  
      /**
       * Request the specified amount of elements from upstream.
       *
       * <p>This method can be called before the upstream calls onSubscribe().
       * When the subscription happens, all missed requests are requested.
       *
       * @param n the request amount, must be positive
       */
      protected final void request(long n) {
          SubscriptionHelper.deferredRequest(s, missedRequested, n);
      }
  
      /**
       * Cancels the subscription (if any) and disposes the resources associated with
       * this AsyncObserver (if any).
       *
       * <p>This method can be called before the upstream calls onSubscribe at which
       * case the Subscription will be immediately cancelled.
       */
      @Override
      public final void dispose() {
          if (SubscriptionHelper.cancel(s)) {
              resources.dispose();
          }
      }
  
      /**
       * Returns true if this AsyncObserver has been disposed/cancelled.
       * @return true if this AsyncObserver has been disposed/cancelled
       */
      @Override
      public final boolean isDisposed() {
          return SubscriptionHelper.isCancelled(s.get());
      }
  }
  